According to the prior art, the air used for cooling a transformer is passed over a series of coils through which water is circulated. The prior art dry transformer cooling coils consist of a series of straight double-walled tubes which terminate at each end in sealed chambered headers. The inner tubes of the straight tubes terminate in one chamber of the header, and the outer tubes terminate in a separate sealed chamber of the header. Cooling fluid is circulated through the inner tubes, and through the corresponding chambers of the headers at each end. Air is passed only over the tubes, and the chambered headers are located outside of the air stream. Any leak in one of the inner tubes is captured by its corresponding outer tube and travels to the separate header chamber at which the outer tubes terminate. Thus, any water from leaks in the inner tubes finds its way to an outer tube chamber in one of the headers. A leak detector is present at the bottom of each of the outer tube chambers to detect the presence of any water. The headers are sealed from one another and from the outside with gaskets, but can be opened for inspection. The disadvantages of this system include the material cost and complex construction of the chambered headers, with outer tubes terminating in one chamber and inner tubes terminating in another chamber. In addition, the chambered headers restrict the ability to efficiently circuit the coil.